composition, fabric construction, and additives. The 1977 Chief of Engineers 

 Civil Works Construction Guide Specification CW 02215 (U.S. Army Corps of 

 Engineers 1977) states that "The plastic yarn shall consist of a long-chain 

 synthetic polymer composed of at least 85 percent by weight of propylene, 

 ethylene, ester, amide or vinylidene chloride." All geotextiles for coastal 

 applications must meet this requirement. Filtering integrity depends on the 

 fabric's ability to resist piping through the fabric and clogging. These 

 properties are discussed in subparagraph c below. These topics are covered 

 in subparagraphs 2c (1) and 2c (2). Filtering integrity also depends on the 

 fabric's resistance to loss of permeability due to distortion of the pores 

 by elongation of the fibers under stress, a physical property of the fabric, 

 or by melting in fire. 



(1) Chemical Stability and Resistance . The first extensive 

 research and testing of geotextiles for filters was by Calhoun during the 

 period 1969 to 1972 (Calhoun, 1972). In the course of his investigations, 

 tests were conducted to determine the chemical stability and resistance of 

 three types of synthetic polymers, polyvinylidene chloride, polypropylene 

 and polyethylene. Further research by Bell and Hicks (1980) also investi- 

 gated chemical properties of these three polymers plus polyester and 

 polyamide. The results of these testing programs established the fact that 

 these synthetics have high chemical stability and resistance to chemical 

 attack (acids and alkalies), and can be used in conventional soil applica- 

 tions with confidence. If the fabric is to be used in an environment 

 containing petroleum products, it is recommended that the geotextile's 

 resistance to these materials also be determined. 



(2) Fabric Construction . Selection of a geotextile for a filter 

 should be based on the filtering and physical properties as well as the 

 chemical properties of the fabric consistent with the site-specific require- 

 ments. Bell and Hicks (1980) found that most fabric engineering properties 

 are more strongly influenced by the fabric construction than the polymer. 

 One of the most extensive and thorough fabric strength testing studies, 

 involving 27 commercially available fabrics, was performed for the Army 

 Engineer District, Mobile, by Haliburton, Anglin, and Lawmaster (1978). It 

 was concluded that fabric construction had more influence than the type of 

 synthetic fiber in the fabric. Because fabric construction is the pre- 

 dominant factor affecting physical properties and filtering performance, 

 three general types of fabric construction are discussed: woven, nonwoven 

 and combination fabrics. 



(a) Woven Fabrics . As the term implies, woven fabrics 

 (commonly called cloths) are manufactured by weaving. Normally, the yarns 

 cross at right angles, overlapped one over the other. The longer direction 

 of the cloth, when it is being woven, is called the warp or machine direc- 

 tion. The narrower direction is referred to as the fill or cross-machine 

 direction. In geotextiles, normally the warp direction is stronger than 

 the fill, although the cloth may be produced with equal strength in both 

 directions or a stronger fill than warp. Filters are woven using a variety 

 of yarns discussed below. 



1_ Monofilament Yarns . Monofilament yarns are a single 

 filament of a polymer, which prohibits absorption of water by the yarn. 

 This was the only type of geotextile used in coastal structures in the 

 United States from 1958 to the mid 1970's. Fabrics woven of monofilament 



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